In the mechanical part industrialization field, designers use computers to design and manufacture mechanical parts. The design of a mechanical part usually involves two steps. The first step is the functional design, which allows the designer to set the shape, dimensions, and features of the part to fulfill a functional specification. Designers usually accomplish this step with the use of Computer Aided Design (“CAD”). CAD programs allow designers to create and view three-dimensional representations of a part. Usually, CAD programs do not design the part based on how the part will be manufactured, but instead based on the functional specification of the part.
The second step in the design of a mechanical part is the part industrialization, which allows the designer to change the shape of the functional part so that it can be manufactured. Designers usually accomplish this step with the use of CAD. The part industrialization step depends on the manufacturing process and ideally saves the functional design of the part. Examples of manufacturing processes include molding, stamping, machining, forging, bending, and welding.
During the part industrialization step of a molding design, the designer usually changes the shape of the functional part to ensure proper manufacturing. FIG. 1 is an example of a designed functional part that needs to be industrialized. The mold for the functional part includes two sides, an upper side 105, and a lower side 106, divided by a parting surface 102. The parting surface 102 is the interface between the upper side and the lower side of the mold, and the two sides 105 and 106 have opposite pulling directions 104. The pulling direction is the directions that the molds of the two sides can be pulled apart. Complex molds can involve more than two sides. These extra sides (also known as slides) can be designed to manufacture details of the part that cannot be formed with just two sides.
Draft angles can be used in the industrialization step to ease the extraction of a new part from the mold, ensure that the mold does not break, and ensure the part does not have bad surface quality. A draft angle can be added to faces in the mold that are parallel to the pulling direction. These faces are drafted (or bended) according to a given angle.
The draft angle typically should not fundamentally change the functional specification of the part. Otherwise, the mechanical specifications of the part can be lost during the manufacturing process. Furthermore, the sides of the drafted part should fit on the parting surface. Otherwise, small and sharp steps can remain on the final part, which, in most cases, have to be removed by hand in expensive post processing.
Small steps can also cause problems when the mold is used in another molding process. FIG. 2 demonstrates an example of this in the sand core problem. FIG. 2a shows the drafted sand core 202 having two sides 204 and 205 separated by a parting surface 201. A small step 203 has been introduced during the industrialization step when the draft angle was added to the two sides. When the two sides of the drafted sand core are used to create the two molds 206 and 207, as is shown in FIG. 2b, the step appears in the final mold. When the hot liquid metal flows around the sand core 208 in the final mold 210, sand can escape from the drafted sand core 208 into the liquid metal, which can ruin the quality of the part.
As is shown in FIG. 5, current CAD systems that manually add the draft angle can require that designers draft the upper sides 502 and lower sides 503 separately. The resulting surfaces of the separately designed part may not fit on the parting surface 501.
Low-level graphic and geometric tools are currently used to change the points and faces of the designed part to implement the draft angle. Such low-level work can take long periods of time and can require many individual user interactions with the design program. These existing techniques involve complex surfacing tools and the skilled user usually has to build the drafted faces and fit the faces on the parting surface manually. This hand made geometry is generally fragile and rework is necessary when modifications are made to the functional part. This invention addresses some of these problems.